elasticsearch/docs/reference/enrich-processor/join-processor.md

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Join	https://www.elastic.co/guide/en/elasticsearch/reference/current/join-processor.html

Join processor [join-processor]

Joins each element of an array into a single string using a separator character between each element. Throws an error when the field is not an array.

$$$join-options$

Name	Required	Default	Description
field	yes	-	Field containing array values to join
separator	yes	-	The separator character
target_field	no	field	The field to assign the joined value to, by default field is updated in-place
description	no	-	Description of the processor. Useful for describing the purpose of the processor or its configuration.
if	no	-	Conditionally execute the processor. See Conditionally run a processor.
ignore_failure	no	false	Ignore failures for the processor. See Handling pipeline failures.
on_failure	no	-	Handle failures for the processor. See Handling pipeline failures.
tag	no	-	Identifier for the processor. Useful for debugging and metrics.

{
  "join": {
    "field": "joined_array_field",
    "separator": "-"
  }
}